Drought Tolerant Perennials: A Toronto Master Gardeners Guide

Lavender (Lavandula spp.) is one of many excellent choices for well-drained soil in full sun. Photo: Helen Battersby

In the gardening world, the term perennial usually refers to an herbaceous perennial, i.e., a plant without woody tissue, that dies back to the ground at the end of the growing season and grows again from its rootstock in spring.

Drought tolerant perennials can be useful to the home gardener for a variety of reasons: climatic conditions, municipal watering restrictions, limited water supply from a well or cistern, water conservation preferences, or lifestyle considerations, such as a cottage garden that must be left unattended for extended periods of time.

Characteristics of Drought Tolerant Perennials

‘Drought tolerant’ is a term used to describe plants that can survive short-term drought because of various adaptations. They may show some of the following characteristics.

Many have silver or grey foliage, resulting from a coating of fine hairs on the surface of their leaves. These hairs reflect light and heat and provide shade, thus reducing the amount of moisture lost to the atmosphere. Waxed or furry leaves, designed to keep plants cool and retain moisture, are also characteristics of many drought tolerant plants.

Leaf size also affects moisture loss. Many plants that have adapted to dry conditions have small or narrow leaves to minimize the amount of exposed leaf surface. Thick leaves are another common adaptation. For this reason, fleshy, succulent plants, such as sedum, are popular choices for dry locations.

Root systems also affect drought tolerance. Perennials with large fibrous roots or deep tap roots are able to reach down into the soil to collect water and store moisture for future use.

Although drought tolerant species may share water-saving adaptations, they can come from a wide range of habitats across the globe, ranging from a Mediterranean climate of cool, damp winters followed by dry, hot summers to the dry woodlands of Southern Europe or the steppes of Central Asia. Many of our resilient summer bloomers are deep-rooted North American tall-grass prairie or savanna plants.  Understanding where your plants come from in the wild can help you find their best location and growing conditions in your garden.

Considerations when choosing drought tolerant perennials

Choose plants suited to the growing conditions of your site. This is always preferable and more successful than attempting to change the site to suit the plant. Plants growing in their preferred locations are much more likely to be healthy than plants growing in less than optimal conditions. A healthy plant is far more likely to be able to withstand disease and pest problems than is a plant that is under stress. Make sure your plants are at least hardy for your gardening zone.

One of the most important factors in choosing plants will be the amount of available sun/shade. As most drought tolerant perennials grow in sunny locations, it is important to understand how light conditions are classified.

  • Full sun – plants require at least 6 hours of direct, late-morning/afternoon sun
  • Partial shade – plants need 4 to 6 hours of morning or afternoon sun, but should be shaded from the hot, midday sun.
  • Full Shade – plants can tolerate less than 4 hours of sun preferably in the morning. A bright location that receives no direct sun would be classified as full shade.

Checking the mature height and spread of your plant will tell you the amount of space it will require in your garden for optimum growth. Overcrowded plants become stressed when competing with neighbouring plants for light, nutrients and moisture. As a result, they are more susceptible to diseases, especially those that are encouraged by poor air circulation.

Native plants are always a good choice when planted in the right soil with appropriate light and moisture. Native plants are already acclimated to our soils and climate, have evolved with the birds and pollinators who use them for shelter and food, and help to increase the local biodiversity. Sunflowers, asters, goldenrods, evening primrose and black-eyed Susan are important plants for bee specialists.

General Care and Maintenance

Until perennials are well established, even drought tolerant plants will need supplemental watering in dry spells. After a few growing seasons, they can usually survive with the water they receive naturally through rainfall.

Perennials that grow in droughty conditions do not need a lot of fertilizer and do best when they receive their nutrients from natural sources, such as compost, decaying leaves or plant debris.

The needs of a rock garden plant growing in full sun are quite different from a shade tolerant groundcover growing in dry shade, such as beside a building or under the canopy of moisture robbing trees. In dry shade locations, a mulch in the form of chopped leaves and/or wood chips laid on the soil’s surface is very important. Mulch forms a barrier which reduces evaporation from the soil below it. The rough surface traps water, preventing runoff, and allows the moisture to drain slowly down into the soil. A layer of mulch will also help suppress weeds. In a sunny rock garden or trough, a layer of gravel mulch might be more appropriate.

Perennials should be dead-headed regularly to keep their appearance tidy and to encourage plants to put their energy into flower production, rather than seeds. Remove diseased plant material promptly and dispose of it off site. Ensuring good air circulation around your plants is also very helpful for avoiding or minimizing most fungal diseases.

The following is a list of recommended drought tolerant plants hardy in Toronto.  Native plants are marked with the letter N.

Recommended Species/Varieties/Cultivars:

Drought Tolerant Perennials for Full Sun:

Groundcovers, rock garden and edging plants:

  • Mount Atlas daisy (Anacyclus pyrethrum depressus)
  • Rock cress, wall cress (Arabis species)
  • Sandwort (Arenaria montana)
  • Thrift, sea pink (Armeria maritima)
  • False rockcress (Aubretia deltoidea)
  • Basket of gold, alyssum (Aurinia saxatilis)
  • Snow in summer (Cerastium tomemtosum)*even though this is not on the invasive species list in Canada, it can be quite aggressive
  • Hardy ice plant (Delosperma nubigenum)
  • Pinks (Dianthus alpinus)
  • Fleabane daisy (Erigeron species)
  • Spurge (Euphorbia myrsinites) (E. polychroma)
  • Rock rose, sun rose (Helianthemum hybrids)
  • Candytuft (Iberis sempervirens)
  • Dwarf bearded iris (Iris pumila)
  • Catmint (Nepeta x faassenii ‘Dropmore Blue’)
  • Ozark sundrops (Oenothera macrocarpa)
  • Douglas moss phlox (Phlox douglasii)
  • Moss phlox, creeping phlox (Phlox subulata)
  • Pincushion flower (Scabiosa japonica var. alpina) (S. ‘Butterfly Blue’)
  • Stonecrop (Sedum acre) – N (S. spurium) – N (S. rupestre) + other dwarf varieties
  • Hens and chicks (Sempervivum tectorum)
  • Thyme (Thymus species)

Medium to tall border perennials:

  • Yarrow (Achillea millefolium) * This plant can be aggressive and persistent
  • Blue star (Amsonia tabernaemontana) (A. hubrichtii)
  • Pearly everlasting (Anaphalis margaritaceae) – N
  • Golden marguerite (Anthemis tinctoria)
  • Silver sage, wormwood (Artemisia ludoviciana)
  • Butterflyweed (Asclepias tuberosa) – N
  • False indigo, wild indigo (Baptisia australis)
  • Perennial cornflower (Centaurea montana)
  • Red valerian (Centranthus ruber)
  • Lanceleaf coreopsis (Coreopsis lanceolata) – N
  • Threadleaf coreopsis (Coreopsis verticillata) – N
  • Seakale (Crambe cordifolia)
  • Pale purple coneflower (Echinacea pallida) – N
  • Purple coneflower (Echinacea purpurea)
  • Sea Holly (Eryngium species)
  • Rattlesnake master (Eryngium yuccifolium)
  • Blanket flower (Gaillardia x grandiflora)
  • Knautia, scabious (Knautia macedonica)
  • Lavender (Lavandula angustifolia)
  • Slender blazing star (Liatris cylindracea) – N
  • Flax (Linum perenne)
  • Rose campion (Lychnis coronaria)
  • Evening primrose (Oenothera biennis) – biennial – N
  • Prickly pear cactus (Opuntia compressa) – N
  • Poppy (Papaver species)
  • Beard-tongue (Penstemon digitalis) – N
  • Hairy penstemon (Penstemon hirsutus) – N
  • Russian sage (Perovskia atriplicifolia)
  • Prairie coneflower, gray headed coneflower (Ratibida pinnata) – N
  • Black-eyed Susan (Rudbeckia hirta) – N
  • Orange coneflower (Rudbeckia fulgida ‘Goldsturm’)
  • Perennial salvia (Salvia nemerosa hybrids)
  • Compass plant (Silphium laciniatum) – N
  • Goldenrod (Solidago speciosa) ( rigida) – N
  • Heath aster (Symphyotrichum ericoides) – N
  • Adam’s needle (Yucca species)

Grasses for full sun

  • Big bluestem (Andropogon gerardii) – N
  • Feather reed grass (Calamagrostis x acutiflora ‘Karl Foerster’)
  • Blue fescue (Festuca glauca)
  • Blue oat grass (Helictotrichon sempervirens)
  • Switch grass (Panicum virgatum) – N
  • Indian grass (Sorghastrum nutans) – N
  • Little blue stem (Schizachyrium scoparium) – N
 Drought Tolerant Perennials for Full Sun or Part Shade:

Groundcovers and low growing perennials:

  • Lady’s mantle (Alchemilla mollis)
  • Canada anemone (Anemone canadensis) – N Spreads readily
  • Wild ginger (Asarum canadense) – N
  • Bergenia (Bergenia cordifolia)
  • Calamint (Calamintha nepeta nepeta)
  • Carpathian bellflower (Campanula carpatica)
  • Strawberry (Fragaria virginiana) (F. vesca) – N
  • Cranesbill (Geranium maculatum) – N
  • Bloody cranesbill (Geranium sanguineum)
  • Prairie smoke (Geum triflorum) – N
  • Creeping phlox (Phlox stolonifera)
  • Woodland phlox (Phlox divaricata) – N
  • Pasque flower (Pulsatilla vulgaris) (P. patens)
  • Barren strawberry (Waldsteinia fragarioides) – N

Medium to tall border perennials:

  • Anise-hyssop, licorice mint (Agastache foeniculum) – N
  • Nodding onion (Allium cernuum) – N
  • Columbine (Aquilegia canadensis) – N
  • Large-leaved aster (Eurybia macrophylla) – N
  • Cranesbill (Geranium maculatum) – N
  • Woodland sunflower (Helianthus divaricatus) – N
  • False sunflower, oxeye sunflower (Heliopsis helianthoides) – N
  • Daylily (Hemerocallis hybrids) * Avoid the invasive wild daylily (H. fulva)
  • Coral bells (Heuchera sanguinea) and hybrids
  • Hosta, plantain lily (Hosta cultivars)
  • Autumn Joy stonecrop (Hylotelephium ‘Herbstfreude’)
  • Common flag, German iris (Iris germanica)
  • False Solomon’s seal (Maianthemum racemosum) – N
  • Wild bergamot (Monarda fistulosa) – N
  • Solomon’s seal (Polygonatum biflorum) – N
  • Grey-stemmed goldenrod (Solidago nemoralis) – N
  • Lamb’s ears (Stachys byzantina)
  • Smooth aster (Symphyotrichum laeve) – N
 Drought Tolerant Perennials for Shade:

Groundcovers and low growing perennials:

  • Canada anemone (Anemone canadensis) – N
  • Wild ginger (Asarum canadense) – N
  • Barrenwort (Epimedium hybrids)
  • Bigroot geranium (Geranium macrorrhizum)
  • Lamium, spotted dead nettle (Lamium maculatum) * choose cultivars rather than the species which could become invasive in natural areas
  • Creeping phlox (Phlox stolonifera)
  • Woodland phlox (Phlox divaricata) – N

Medium to tall border perennials:

  • Large-leaved aster (Eurybia macrophylla) – N
  • Zigzag goldenrod (Solidago flexicaulis) – N
  • False Solomon’s seal (Maianthemum racemosum) – N
  • Solomon’s seal (Polygonatum biflorum) – N

Ferns for dry shade

  • Hay-scented fern (Dennstaedtia punctilobula) – N
  • Marginal wood fern (Dryopteris marginalis) – N
  • Male fern (Dryopteris filix-mas) – N
  • Rock fern (Polypodium virginianum) – N
  • Christmas fern (Polystichum acrostichoides) – N

Invasive Species

Many lists of drought tolerant perennials will include perennials such as the wild daylily (Hemerocallis fulva), Japanese spurge (Pachysandra terminalis), yellow archangel (Lamiastrum galeobdolon) and spotted dead nettle (Lamium maculatum). These invasive plants can spread into natural areas and have an adverse effect on local native plants. For this reason, they are not recommended. For information about invasive plants and non-invasive alternatives, see the link below to the Grow Me Instead brochure.

References

Grow Me Instead: beautiful non-invasive plants for your garden. Ontario Invasive Plants Council, 2020.  https://www.ontarioinvasiveplants.ca/wp-content/uploads/2020/04/Southern-Grow-Me-Instead-1.pdf

Healthy Landscapes – Plant list: Native and drought tolerant plants https://guelph.ca/wp-content/uploads/droughtTolerant-NativePlants.pdf

Halton Master Gardeners.  Sources for Native Plants in Southern Ontario (map) https://www.google.com/maps/d/viewer?mid=1dHiK77VTR2EKZXbXoKdTctGGZDVvPqeJ&ll=43.64984724339944%2C-79.5650104&z=8

Bennett, Jennifer. Dry-Land Gardening. Willowdale, Ontario: Firefly Books Ltd., 1998

Damrosch, Barbara. The Garden Primer. New York, NY: Workman Publishing Company, Inc., 1988

Valleau, John. Perennial Gardening Guide. Abbortsford, British Columbia: Valleybrook International Ventures Inc. 2003.

Date revised: October 2021

Prepared by the Toronto Master Gardeners, these Gardening Guides provide introductory information on a variety of gardening topics.  Toronto Master Gardeners are part of a large, international volunteer community committed to providing the public with horticultural information, education and inspiration.  Our goal is to help Toronto residents use safe, effective, proven and sustainable horticultural practices to create gardens, landscapes and communities that are both vibrant and healthy.

Statement on Invasive Plants: When choosing plants, avoid invasive plants, which can spread quickly and dominate gardens.  Invasive plants are sold by nurseries, big box stores or even at community plant sales.  Invasives may already be present in your garden.  They can invade gardens by spreading from under a neighbour’s fence or may be transported by wildlife.  For beautiful, sustainable options to invasive plants, see the Ontario Invasive Plant Council’s “Grow Me Instead – Beautiful Non-Invasive Plants for your Garden” at https://www.ontarioinvasiveplants.ca/resources/grow-me-instead/ before purchasing or accepting “gifts” of plants.

Statement on Home Remedies: The Toronto Master Gardeners do not recommend home remedies, as these have not been proven effective through scientific investigation, and may even damage other living organisms in the soil or plants in your garden.  There are other garden friendly options you can use.

If you have further gardening questions, reach us at our gardening advice line 416 397 1345 or by posting your question here in the Ask a Master Gardener section.  To book Toronto Master Gardener volunteers for talks, demonstrations, advice clinics, or other services, please contact us at 416 397 1345  or bookamg@torontomastergardeners.ca.